In recent years, flat display devices such as liquid crystal display devices or organic EL display devices are widely used as display devices for televisions, mobile phones, smartphones, and the like, for example. Such flat display devices are provided with a driver circuit (typically, a driver IC chip) for supplying driving signals to a display panel. In many cases, the display panel has at least one transparent substrate, and an IC chip having a driver circuit formed thereon is mounted on the transparent substrate.
A TFT liquid crystal display device, for example, has a glass substrate, and the glass substrate has formed thereon: pixel electrodes provided for respective pixels; TFTs provided such that each pixel electrode has at least one TFT; signal lines (source bus lines) connected to the pixel electrodes via the TFTs; and scan lines (gate bus lines) connected to the TFTs for controlling the switching of the TFTs. The driver IC chip for supplying prescribed signals (data signals and scan signals) to the signal lines and the scan lines is mounted on the same glass substrate (TFT substrate).
In terms of the mounting structure for the driver IC chip, a COG (chip on glass) method has been used in recent years because of the advantages thereof such as low cost, high reliability, and thickness reduction. In the COG method, the driver IC chip as a bare chip is mounted on the glass substrate of the liquid crystal panel. Other known methods include a COF method in which the driver IC chip is mounted on a film.
One known example of the COG method is a so-called face-down mounting structure in which protruding bump electrodes are formed on the surface of the driver IC chip where circuits are formed, and the bump electrodes are connected to respective pads (connecting terminal electrodes of scan lines or signal lines; also referred to as bonding pads) formed on a glass substrate of a liquid crystal panel. In this mounting structure, the bump electrodes are formed of a metal such as Au, for example, and are connected to the pads through an anisotropic conductive layer, for example.
Because the anisotropic conductive layer has conductivity only in the thickness direction, and not in the horizontal direction, it is not necessary to pattern the conductive layer, and the bump electrode and the pad facing each other can be electrically connected to each other through the anisotropic conductive layer. Also, because a gap between respective adjacent electrodes is filled with a resin material (adhesive material), it is possible to achieve excellent insulating properties. The anisotropic conductive layer is formed of an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), or the like.
FIG. 10 shows a conventional chip mounting structure 900 in which a driver IC chip 920 is mounted in an edge of the liquid crystal panel with the face-down mounting. As shown in the figure, the driver IC chip 920 is connected to a TFT substrate 910 of the liquid crystal panel through an ACF 930. More specifically, bump electrodes 922 provided on the IC chip 920 and connecting terminals (pads) 912 provided on the TFT substrate 910 are electrically connected to each other via conductive particles 932 included in the ACF 930 provided between the IC chip 920 and the TFT substrate 910. By the resin material of the ACF 930 being cured, the IC chip 920 is affixed onto the TFT substrate 910.
Various techniques have been proposed for connecting an electronic component such as an IC chip to a wiring substrate such as a TFT substrate, and for example, a technique for improving the connection reliability by using an elastic body (resin material, for example) is known.
Patent Document 1 shows a structure in which a mounting substrate for an electronic component has a recess, and an electronic component is placed inside of the recess such that a conductive elastic body is interposed between the electronic component and the side faces of the recess. In this electronic component mounting structure, the electronic component is pressed toward the side faces of the recess by the elastic body, and connecting electrodes at the side faces of the recess and electrodes at the side faces of the electronic component are more reliably connected to each other.
Patent Document 2 discloses a configuration in which each pad is disposed on the chip mounting substrate through a protruding elastic body. In this manner, it is possible to achieve a high bonding property when the chip is mounted, regardless of the rigidity of the substrate. Patent Document 3 discloses a configuration in which a resin layer is provided on a mounting substrate, and an IC chip is connected to the substrate in such a manner that bump electrodes are connected to electrodes formed on the resin layer, while sinking into the resin layer.